2nd LD - What Caused It?

last night i had my second LD. in my dream, i was in my friend's room. for some reason, i thought "i shouldn't be here, this is going to make me wake up". i dont know what made me realize it was a dream.

i dont remember questioning reality, or thinking about whether or not it was a dream. i already KNEW it was a dream and the only thought i had was that being in that room would wake me up. i think i jumped from a non-lucid in another place, directly into my friend's room.

after that very short LD, i had my first false awakening. i got up, went to the bathroom, went back to bed and woke up for real. any ideas on why i instantly knew it was a dream when i found myself in my friend's room? im pretty sure the dream started with me already in the room, knowing it was a dream.

you don't remember getting there

also, how do you know this isn't a dream?
dun-dun-dun-duuuhhhh

One thing helps just train yourself to beaware eventually you wont need dreamsigns like Oh i shoudnt be here.... its in another country so or so